Synthetic biology aims to study the control of gene expression by constructing gene regulation systems from the “bottom-up” in order to better understand natural biological systems and develop useful tools for biotechnology. Despite many significant accomplishments, this field has largely been limited to studying artificial promoter transgene systems with one or two transactivators, typically in microorganisms. In contrast, the natural regulation of mammalian gene expression is extraordinarily complex. This level of complexity has not yet been achieved in synthetic gene regulation systems and has not been possible for the regulation of endogenous genes.
Several TALE-TFs have recently been reported to regulate native mammalian gene expression. However, the recent emergence of technologies for engineering transcription activator-like effectors (TALEs) targeted to almost any DNA sequence provides a unique opportunity for recapitulating this natural complexity. However, the levels of gene activation in these studies were modest and several genes could not be induced (Table 1). Therefore there is clear need for improvements to gene activation strategies that capitalize on the synthetic TALE-TF technology.
TABLE 1Published TALE-TFs Targeting Human Genes.ActivationFold-ReferenceGeneDomainAssayIncreaseZhang et al., NatureSOX2VP64qRT-PCR5.5Biotechnology (2011)KLF4VP64qRT-PCR2.2MYCVP64qRT-PCRn.d.OCT4VP64qRT-PCRn.d.Miller et al., NatureNTF3VP16qRT-PCR30Biotechnology (2011)Geissler et al.,PUMAVP16qRT-PCR1.5PLoS One (2011)IFNA1VP16qRT-PCR3IFNB1VP16qRT-PCR3.5Bultmann et al., NucleicOCT4VP16qRT-PCR n.d.1Acids Research (2012)Cong et al., NatureCACNA1CVP64qRT-PCR3-5Communications (2012)Tremblay et al., HumanFXNVP64qRT-PCR1.1-3.1Gene Therapy (2012)Garg et al., NucleicOSGIN2VP64qRT-PCR4.8Acids Research (2012)ZC3H10VP64qRT-PCR1.3n.d. = not detected1undetectable in control, induced only with chromatin-modifying drugs